Cell elongation, either due to spread or stretch, induces lung embryonic mesenchymal cells to follow a myogenic pathway [1-3]. Using these systems we identified by suppressive subtraction hybridization (SSH) two similar stretch-responsive factors, which we referred to as tension-induced/inhibited proteins (TIPs) -1 and -3. A third isoform of intermediate Mf/, TIP-2, was identified in the GenBank, hut it was not present in the lung. A Genomic BLAST search indicated that the three TIPs were originated by alternative splicing from a single gene. Immunohistochemical studies and tagging with green fluorescence protein (GFP) demonstrated that TIPs translocate between nucleus and cytoplasm. TIPs display signature motifs characteristic of nuclear receptor coregulators and chromatin remodeling enzymes. Functional studies encompassing overexpression of TIPs and gene silencing using small interfering RNAs (siRNA) indicated that TIP-1 and -3 are involved in the cell's selection between the myogenic and adipogenic pathways. TIP- 1, induced by stretch, promotes myogenesis while TIP-3, inhibited by tension initiates adipogenesis. Furthermore, chromatin immunoprecipitation (ChIP) assays indicated that TIPs may act through a mechanism of chromatin remodeling. Since the lung has bronchial smooth muscle (SM), interstitial myofibroblasts and lipofibroblasts, we hypothesize that the development of these cell types is determined at least in part by TIPs. The specific aims of this project will be: Aim 1. To determine whether modulation of TIP-1 and TIPS alters bronchial SM, myofibroblasts and lipofibroblasts development in lung organ cultures and organotypic cultures. Aim 2. To elucidate the transcription factors that are activated by TIP-1 and TIP-3 and whether gene acetylation, methylation or both are involved in TIP-induced transcription activation. Aim 3. To identify the histone(s) that bind(s) to TIPs and to determine the TIP motifs that are required for histone-TIP binding. Bronchial and vascular SM, myofibroblasts and lipofibroblasts are essential components of the lung. These cells participate in multiple physiological processes and however very little is known about their development and the molecular mechanisms involved in their genesis. The studies proposed in this application will provide therefore novel information on how the myogenic and adipogenic fates are determined in the embryonic lung at the cellular and molecular level.